• Journal of Positioning, Navigation, and Timing
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• v.4 no.2
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• pp.67-72
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• 2015

Power grid techniques are distributed over general power systems ranging from power stations to power transmission, power distribution, and users. To monitor and control the elements and performance of a power system in real time in the extensive area of power generation, power transmission, wide-area monitoring (WAM) and control techniques are required (Sattinger et al. 2007). Also, to efficiently operate a power grid, integrated techniques of information and communication technology are required for the application of communication network and relevant equipment, computing, and system control software. WAM should make a precise power grid measurement of more than once per cycle by time synchronization using GPS. By collecting the measurement values of a power grid from substations located at faraway regions through remote communication, the current status of the entire power grid system can be examined. However, for GPS that is used in general national industries, unexpected dangerous situations have occurred due to its deterioration and jamming. Currently, the power grid is based on a synchronization system using GPS. Thus, interruption of the time synchronization system of the power system due to the failure or abnormal condition of GPS would have enormous effects on each field such as economy, security, and the lives of the public due to the destruction of the synchronization system of the national power grid. Developed countries have an emergency substitute system in preparation for this abnormal situation of GPS. Therefore, in Korea, a system that is used to prepare for the interruption of GPS reception should also be established on a long-term basis; but prior to this, it is required that an evaluation technique for the time synchronization performance of a GPS receiver using an atomic clock within the power grid. In this study, a monitoring system of time synchronization based on GPS at a power grid was implemented, and the results were presented.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.2
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• pp.228-231
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• 2015

In power system research fields, one of current key issues is the construction and commercialization of micro grid site which is called green island, carbon zero island, energy independent island, building micro grid, etc. and various affiliated technologies have been being vigorously developed to realize. In addition, various researches about electric vehicles (EVs) are in progress and it is expected to penetrate rapidly with the next a few years. Some new load models should be developed integrating with electric vehicle loads because the EVs' deployment could cause the change of load composition rate on power system planning and operations. EVs are also resources for micro grid as well as distributed generation and demand response so that various supply and demand side resources should be considered for micro grid researches. In this paper, the load composition rate of residential sectors is prospected considering the deployment of EVs and the resource configuration of micro grid is optimized based on net present cost. In the optimization, the load patten of case studies includes EV's charging characteristics and various cases are simulated comparing micro grid environment and normal condition. HOMER is used to compare various cases and economic effects.

• Korean Journal of Digital Imaging in Medicine
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• v.14 no.2
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• pp.47-56
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• 2012

Amount of radiation exposure by seeing through fluoroscopy examination while is many patient exposure administration and unprepared misgovernment be. In this study, abdominal fluoroscopy during the scan, the dose and image quality change according to the use of grid and added filter optimized by measuring the test condition is proposed. Uses seeing through fluoroscopy examination equipment of Image Intensifier of Easy Diagnost Eleva (Philips), under tube type and uses Human phantom and measures average area dose according to grid insertion existence and nonexistence and added filter kind change. Measure sum of 29 organ dose and effective dose through PCXMC imagination simulation program and image J program through noise, SNR, image distortion was measured. Resolution, sharpness, and analyzed using the MTF curves. Fluorography the grid to insert the filter thickness and thickening and increased the average area dose and organ doses and effective dose. In the case of spot examination, when inserted grid, average area dose and organ dose and effective dose increased. Filter thickens the average area dose decreased, but the organ doses and effective dose were increased when use 0.2mmCu+1mmAl filter, decreased slightly. Noise and SNR measurements without inserting the gird, if you do not use the added filter was the lowest and when measure the distortion, 0.1mmCu+1mmAl filter was no difference of image quality in case insert grid was judged that when did not use occasion added filter that do not use grid, difference of image quality does not exist. Did not show a big difference, according to the grid and uses of the added filter sharpness, and resolution. Patient dose increases with factors that reduce the quality of the image so reckless grid and the use of the added filter when abdominal fluoroscopy examination should be cautious in using.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.6
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• pp.703-712
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• 1999

This paper suggests an automatic elliptic grid generation method that is well-suited for the numerical mapping of complex geometries which are easily obtained from general CAD programs. An LBLADI solver is used for the governing mapping equations to have the strong diagonal dominance. The full boundary control method is adopted to determine the control functions of the equations, which allows the control of the grid regarding spacing and angle control at all boundary surfaces. The solution method presented here provides the capability of mapping very complicated geometries by defining grid point locations only along the boundaries. In the automated elliptic grid generation procedure, it is showed that strong diagonal dominance is essential to achieve successful mapping irrespective of the initial grid condition provided. To demonstrate the robustness of this method, it is applied to the thermal flow like the natural convection between eccentric cylinders. The results agree well with others.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2558-2562
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• 2007

In the present work, flow characteristics analysis has been performed for steam turbine bypass control valve (single-path type). The numerical analysis is performed by solving three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations. Shear stress transport (SST) model is used as turbulence closure. Symmetry condition is applied at the mid plane of the valve while adiabatic condition is used at the outer wall of the cage. Grid independency test is performed to find the optimal number of grid points. The pressure and temperature distributions on the outer wall of the cage are analyzed. Mass flow rate at maximum plug opening condition is compared with the designed mass flow rate.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.9
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• pp.33-41
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• 2015

To improve the power quality of distributed generation (DG) systems even in the presence of distorted grid condition, dual current control scheme of a grid-connected inverter is proposed. The proposed current control scheme is achieved by decomposing the inverter state equations into the fundamental and harmonic components. The derived models are employed to design dual current controllers. The conventional PI decoupling current controller is used in the fundamental model to control the main power flow in DG systems. At the same time, the predictive control is applied in the harmonic model to suppress undesired harmonic currents to zero quickly. To decompose the voltage inputs and state variables into the fundamental and harmonic components, the fourth order band pass filter (BPF) is designed in the discrete-time domain for a digital implementation. For experimental verification, 2kVA prototype of a grid-connected inverter has been constructed using digital signal processor (DSP) TMS320F28335. The effectiveness of the proposed strategy is demonstrated through comparative simulation and experimental results.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.344-345
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• 2018

In order to alleviate the negative impacts of harmonically distorted grid condition on grid-connect inverters, an optimal control design-based gain selection scheme of an LCL-filtered grid-connected inverter and its ability to compensate selective harmonics are presented in this paper. By incorporating resonant terms into the control structure in the state-space to provide infinity gain at selected frequencies, the proposed control offers an excellent steady-state response even under distorted grid voltage. The proposed control scheme is achieved by using a state feedback controller for stabilization purpose and by augmenting the resonant terms as well as intergral term into a control structure for reference tracking and harmonic compensation. Furthermore, the optimal linear quadratic control approach is adopted for choosing an optimal feedback gain to ensure an asymptotic stability of the whole system. A discrete-time full state observer is also introduced into the proposed control scheme for the purpose of reducing a total number of sensors used in the inverter system. The simulation results are given to prove the effectiveness and validity of the proposed control scheme.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.183-191
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• 2009

Finite difference method using not general SSG (standard staggered grid) but RSG (rotated staggered grid) was applied to simulation of elastic wave propagation. Special free surface boundary condition such as imaging method is needed in finite difference method using SSG in elastic wave propagation. But free surface boundary condition in finite difference method using RSG is easily solved with adding air layer or vacuum layer. Recently PML (Perfectly Matched layer) is widely used to eliminate artificial reflection waves from finite boundary because of its' greate efficiency. Absorbing ability of CPML (convolutional Perfectly Matched Layer) that is more efficient than that of PML and CPML that don't use splitting of wave equation that should be adapted to PML was applied to FDM using RSG in this study. Frequency absorbing characteristic and energy absorbing ability in CPML layer were investigated and CPML eliminated artificial boundary waves very effectively in FDM using RSG in being compared with that of Cerjan's absorbing method. CPML method also diminished amplitude of waves in boundary layer of solid-liquid model very well.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.367-368
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• 2014

This paper investigates characteristics of high power semiconductor device losses in 5MW-class Permanent Magnet Synchronous Generator (PMSG) Medium Voltage (MV) wind turbines. High power semiconductor device of press-pack type IGCT of 6.5kV is considered in this paper. Analysis is performed based on neutral point clamped (NPC) 3-level back-to-back type voltage source converter (VSC) supplied from grid voltage of 4160V. This paper describes total loss distribution at worst case under inverter and rectifier operating mode for the power semiconductor switches. The loss analysis is confirmed through PLECS simulations. In addition, the loss factors due to di/dt snubber and ac input filter are presented. The investigation result shows that IGCT type semiconductor devices generate the total efficiency of 97.74% under the rated condition.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.5
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• pp.417-422
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• 2008

In this paper, a novel DC/DC low-voltage high-current converter circuit is proposed to improve the efficiency of power converter used in the grid-connected fuel-cell generator system. We proposed a novel high efficiency grid-connected power conditioning system for RPG fuel cell. On the result of that, the loss of system was decreased rapidly by driving stack within the condition of maximum efficiency. The peak currents of the current-type inductor and the transformer's coil are reduced by synchronizing switching frequency of Buck-type converter is increased twice as the Push-Pull converter's switching frequency. The novel structure of DC/DC converter is able to realize ZVS-ZCS in fuel-cell system is proposed. The proposed switching component of Push-Pull converter has the ZVS and ZCS function by using the circuit of new passive clamp.